They go further: as ever larger numbers of people increase the size of of towns and cities, 60 percent of all humanity will be urbanized by 2030.

By then, the seductions of city life are forecast to have embraced 5 billion people, up from 2.9 billion in 2000. Most all of the population increase that the UN expects in this period will be absorbed by urban areas of the developing countries -- cities already blighted, in the popular image, by widespread slums, inadequate health services, not enough schools, and plain old grinding poverty.

As cities continue their explosive growth, rural populations in the less developed regions of the world are expected to show an increase also, but very slowly, the Population Division of the UN Department of Economic and Social Affairs says in its just released revised report on the prospective consequences of urbanization.

Joseph Chamie, the division head, is an acknowledged global authority on demographics and his and the division's past projections have been extraordinarily accurate. In an interview Thursday for UN TV, he cautioned, however, that there now are so many new variables out there, including the impact of the AIDS pandemic, that the division's reputation for calling the shots correctly (to within a fraction of a percentage point) may prove hard to sustain in the next few years. Still, if anybody can keep up with the trends, it's the articulate Chamie and his dedicated crew.

It's no secret that in regions where economic development is far advanced, urbanization is, too; and 75 percent of these regions' population was estimated to be living in towns and cities at the dawn of the new millennium. That share is projected to rise to 84 percent by 2030. In the less developed countries, by the same year, 56 percent of their inhabitants is expected to live in cities.

The UN report points to marked differences in the level and pace of urbanization among the major areas that constitute the world's less developed regions. (Developent and underdevelopment are terms that used to cause semantic problems for the UN, which is why the word developing now is favored when speaking of poorer, nonindustrialized states.)

Latin America and the Caribbean (largely, if not all, developing countries) are highly urbanized as a whole, the UN report notes, with three-fourths of their populations living in "urban settlements" in 2000 -- an urban share higher than that in Europe, and twice the UN estimate for urbanization in Africa or Asia. Those two continents are projected to play catch-up in the next two or more decades, however, with their urban populations rising to 53 and 54 percent respectively. But by then, says the UN, Latin America and the Caribbean lands will have leapt ahead some more, to 84 percent -- about the level for 2030 in North America, the most highly urbanized region.

Despite all of the grim tales of teeming millions living in densely packed squalor in third world cities, the proportion, globally, of inhabitants of these urban agglomerations, as they are called, is actually quite small, the UN's numbers demonstrate. In 2000, it was 3.7 percent and it's projected to rise only by one full percentage point, to 4.7 percent, by 2015.

But the 24.8 percent that lived in cities of under 500,000 in 2000 is expected to increase to 27.1 percent by 2015. Some of the fastest growing cities have relatively small populations now, the report says. As population increases, the growth rate tends to decline.

With 26.5 million residents, Tokyo leads the world populationwise, followed by Sao Paulo and Mexico City (18.3m. each), Metropolitan New York (16.8m.) and Bombay (16.5m.). London, once the most populous city in the world, dropped out of the leadership race long ago.

Tokyo is projected to retain its preeminence in 2015, with 27.2m. inhabitants, exceeding Dhaka, Bombay, Sao Paulo, Delhi and Mexico City -- each with more than 20m. population.